Method to Determine the Mass of Air Trapped in Each Cylinder of an Internal Combustion Engine

Abstract

A method to determine the mass of air trapped in each cylinder of an internal combustion engine, which comprises determining, based on a model using measured and/or estimated physical quantities, a value for a first group of reference quantities; determining, based on the model, the actual inner volume of each cylinder as a function of the speed of rotation of the internal combustion engine and of the closing delay angle of the intake valve; and calculating the mass of air trapped in each cylinder as a function of the first group of reference quantities and of the actual inner volume of each cylinder.

1 . A method to determine the mass (m) of air trapped in each cylinder ( 3 ) of an internal combustion engine ( 1 ); wherein the internal combustion engine ( 1 ) comprises a number of cylinders ( 3 ), each connected to an intake manifold ( 4 ), from which it receives fresh air through at least one respective intake valve ( 5 ), and to an exhaust manifold ( 6 ), into which it introduces the exhaust gases produced by the combustion through at least one respective exhaust valve ( 7 ); and wherein the intake valves ( 5 ) and/or the exhaust valves ( 7 ) are controlled so as to change the timing thereof; the method comprises:
 determining, based on a filling model using measured and/or estimated physical quantities, a value for a first group of reference quantities including:   P pressure measured for the engine cycle inside the intake manifold ( 4 );   n speed of rotation of the internal combustion engine ( 1 );   OFF mass of gases produced by the combustion in the previous work cycle and present inside the cylinder ( 3 );   IVC closing delay angle of the intake valve ( 5 );   determining, based on said filling model, the actual inner volume (V) of each cylinder ( 3 ) as a function of the speed (n) of rotation of the internal combustion engine ( 1 ) and of the closing delay angle (IVC) of the intake valve ( 5 ); and   determining the mass (m) of air trapped in each cylinder ( 3 ) as a function of the first group of reference quantities and of the actual inner volume (V) of each cylinder ( 3 ) through the following equation:
     m=P*V−OFF   [5];
 
   calculating the mass of gases (OFF) produced by the combustion in the previous work cycle and present inside the cylinder ( 3 ), in case the pressure of the intake manifold ( 4 ) exceeds the pressure in the exhaust manifold ( 6 ), through the following equation:
     OFF=P   EXH   *V   CC /( R*T   EXH )− M   EXH_SCAV   [16]
 
   P EXH  pressure of the gas flow in the exhaust;   T EXH  temperature of the gas flow in the exhaust;   V CC  volume of the combustion chamber of the cylinder ( 3 );   M EXH_SCAV  residual mass of exhaust gases present inside the combustion chamber of the cylinder ( 3 ) and directly directed towards the exhaust manifold ( 6 ) through the respective exhaust valve ( 7 ); and   R constant of the mixture of fresh air and/or exhaust gases.   
     
     
         2 . The method according to  claim 1 , wherein the internal combustion engine ( 1 ) comprises a low-pressure gas recirculation circuit; the method comprises the further steps of:
 calculating a quantity (R EGR ) indicating the incidence of a low-pressure circuit on the gas mixture flowing in an intake duct ( 6 ):
     R   EGR   =M   EGR_LP   /M   TOT   [2]
 
   M TOT  mass of the gas mixture flowing through the intake duct ( 6 );   M EGR  LP mass of exhaust gas recirculated through the low-pressure circuit, which flows in the intake duct ( 6 ); and   calculating the mass of gases (OFF) produced by the combustion in the previous work cycle and present inside the cylinder ( 3 ) by means of the following equation:
     OFF=P   EXH   *V   CC /( R*T   EXH )− M   EXH_SCAV *(1− R   EGR )
 
   
     
     
         3 . The method according to  claim 1  and comprising the further step causing the mass of gases (OFF) produced by the combustion in the previous work cycle and present inside the cylinder ( 3 ) to be equal to zero, in case the entire flow rate of gases produced by the combustion in the previous work cycle and present inside the cylinder ( 3 ) is directly directed towards the exhaust manifold ( 6 ) during the overlap phase through the respective exhaust valve ( 7 ). 
     
     
         4 . The method according to  claim 1  and comprising the further step of calculating said residual mass (M EXH_SCAV ) of exhaust gases as a function of the mass (M OVL ) flowing from the intake to the exhaust through the intake valve ( 5 ) and the exhaust valve ( 7 ). 
     
     
         5 . The method according to  claim 4 , wherein said residual mass (M EXH_SCAV ) of exhaust gases is calculated as a function of the speed (n) of rotation of the internal combustion engine ( 1 ). 
     
     
         6 . The method according to  claim 1 , wherein said residual mass (M EXH_SCAV ) of exhaust gases is calculated as a function of the pressure (PEW and of the temperature (T EXH ) of the gas flow in the exhaust and of the volume (V CC ) of the combustion chamber of the cylinder ( 3 ). 
     
     
         7 . The method according to  claim 3 , wherein said residual mass (M EXH_SCAV ) of exhaust gases is calculated by means of the following equation:
     M   EXH_SCAV   =f ( M   OVL   ,n )* P   EXH   *V   CC /( R*T   EXH )  [14]
   P EXH , T EXH  pressure and temperature of the gas flow in the exhaust;   V CC  volume of the combustion chamber of the cylinder ( 3 );   n speed of rotation of the internal combustion engine ( 1 );   M OVL  mass flowing from the intake to the exhaust through the intake valve ( 5 ) and the exhaust valve ( 7 );   R constant of the mixture of fresh air and/or exhaust gases.   
     
     
         8 . The method according to  claim 3 , wherein said residual mass (M EXH_SCAV ) of exhaust gases is calculated by means of the following equation:
     M   EXH_SCAV   =M   OVL   *f ( M   OVL   ,n )* g   2 ( G,n )   n speed of rotation of the internal combustion engine ( 1 );   M OVL  mass flowing from the intake to the exhaust through the intake valve ( 5 ) and the exhaust valve ( 7 ); and   G centre of gravity of the overlap phase.   
     
     
         9 . A method according to  claim 1 , wherein said mass (M OVL ) flowing through the overlap, namely through the intake valve ( 5 ) and the exhaust valve ( 7 ) is determined by means of the following equation:
     M   OVL   =A*G *β( P/P   0   ,n )* P   0   /P   0_ REF*( T   0_REF   /T   0 ) 1/2   /n   [12]
   A*G hydraulic permeability of the overlap;   n speed of the internal combustion engine ( 1 );   P 0_ REF reference pressure upstream of the passage section (or overlap);   T 0_REF  reference temperature upstream of the passage section (or overlap);   T 0  temperature upstream of the passage section (or overlap);   P 0 , P pressure upstream and downstream, respectively, of the passage section (or overlap).   
     
     
         10 . The method according to  claim 1 , wherein the mass (m) of air trapped in each cylinder ( 3 ) is calculated as a function of a number of multiplying coefficients (K 1 , K 2 ), which take into account the angular extent (VVT I ) of a difference relative to the reference values of the intake valve ( 5 ), the angular extent (VVT E ) of a difference relative to the reference values of the exhaust valve ( 7 ) and the speed (n) of rotation of the internal combustion engine ( 1 ). 
     
     
         11 . The method according to  claim 10 , wherein the mass (m) of air trapped in each cylinder ( 3 ) is calculated as a function of a first multiplying coefficient (K 1 ), which takes into account the angular extent (VVT I ) of a difference relative to the reference values of the intake valve ( 5 ) and the angular extent (VVT E ) of a difference relative to the reference values of the exhaust valve ( 7 ), and of a second multiplying coefficient (K 2 ), which takes into account the speed (n) of rotation of the internal combustion engine ( 1 ) and the angular extent (VVT E ) of a difference relative to the reference values of the exhaust valve ( 7 ). 
     
     
         12 . The method according to  claim 1 , wherein the internal combustion engine ( 1 ) further comprises an EGR exhaust gas recirculation circuit (EGR LP , EGR HP ), which comprises, in turn, a bypass duct ( 34 ,  26 ); along the bypass duct ( 34 ,  26 ) there is arranged an EGR valve ( 35 ,  27 ), which is designed to adjust the flow rate of the exhaust gases flowing through the bypass duct ( 34 ,  26 ); the method comprises determining the mass (m) of air trapped in each cylinder ( 3 ) as a function of a mass (M EGR ) recirculated through the EGR circuit (EGR LP , EGR HP ) for each cylinder ( 3 ). 
     
     
         13 . The method according to  claim 12 , wherein the mass (m) of air trapped in each cylinder ( 3 ) is calculated by means of the following formula:
     m =( P*V−OFF )* f   1 ( T,P )* f   2 ( T   H2O   ,P )*− M   EGR   [22]
   f 1  f 2  functions taking into account the temperature (T) inside the intake manifold ( 4 ), the intake pressure (P) and the temperature (T H2O ) of the coolant fluid of the internal combustion engine ( 1 );   OFFmass of gases produced by the combustion in the previous work cycle and present inside the cylinder ( 3 );   M EGR  mass (M EGR ) recirculated through the EGR circuit (EGR LP , EGR HP ) for each cylinder ( 3 ).   
     
     
         14 . The method according to  claim 1 , wherein the volume (V CC ) of the combustion chamber of the cylinder ( 3 ) is a function of the speed (n) of rotation of the internal combustion engine ( 1 ) and of a first parameter (TVC), which is alternatively equal to the closing delay angle (EVC) of the exhaust valve ( 7 ) or to the greatest value between zero and the smallest value between the closing delay angle (EVC) of the exhaust valve ( 7 ) and the value of the opening advance angle (IVO) of the intake valve ( 5 ) multiplied by −1. 
     
     
         15 . The method according to  claim 1 , wherein the volume (V CC ) of the combustion chamber of the cylinder ( 3 ) is determined by means of a third map, which is a function of the speed of rotation (n) of the internal combustion engine ( 1 ) and of the first parameter (TVC), and by means of a fourth map, which is a function of the speed (n) of rotation of the internal combustion engine ( 1 ) and of the duration (OVL) of the overlap phase. 
     
     
         16 . The method according to  claim 1  and comprising the further steps of:
 determining, based on a calculation model using measured and/or estimated physical quantities, the mass (m obj ) of combustion air needed by each cylinder ( 3 ) in order to fulfil the torque request (C t *); and 
 determining the objective pressure value (Pow) inside the intake manifold ( 4 ) based on said filling model as a function of the mass (m obj ) of combustion air needed by each cylinder ( 3 ) in order to fulfil the torque request (C t *), of the actual inner volume (V) of each cylinder ( 3 ) and of the first group of reference quantities. 
 
     
     
         17 . The method according to  claim 16 , wherein the internal combustion engine ( 1 ) comprises a valve ( 12 ), which is designed to adjust the flow rate of the gas mixture comprising both exhaust gases and fresh air, i.e. air coming from the outside, through the intake duct ( 8 ), directed towards the intake manifold ( 4 ); the method comprises controlling said valve ( 12 ) so as to obtain the objective pressure value (P OBJ ) inside the intake manifold ( 4 ).